Image sensor and method for fabricating the same

ABSTRACT

An image sensor includes a semiconductor substrate, a plurality of photoelectric transducer devices and a dielectric isolating structure. The semiconductor substrate has a backside surface and a front side surface opposite to the backside surface. The photoelectric transducer devices are disposed on the front side surface. The dielectric isolating structure extends downwards into the semiconductor substrate from the front side surface and penetrates through the backside surface, so as to from a grid structure and isolate the photoelectric transducer devices from each other.

This application claims the benefit of People's Republic of Chinaapplication Serial No. 201510477505.1, filed Aug. 6, 2015, the inventionof which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The invention relates in general to a semiconductor device and themethod for fabricating the same, and more particularly to an imagesensor and the method for fabricating the same.

BACKGROUND

An image sensor, such as a metal-oxide-semiconductor (MOS) image sensor,is a device that converts an optical image into an electric signal andhas been commonly used in the consumer electronics that require highresolution, such as digital cameras, apparatuses for applying personalcommunications service (PCS), game equipment, etc.

In order to realize higher resolution and satisfy the requirements ofthe consumer electronics. Pixel density of an image sensor may beincreased and the size and pitch of the photoelectric transducerdevices, such as photodiodes, that are involved in the image sensor maybe shrank. However, the shrinkage in the pitch of the photoelectrictransducer devices may cause electrical and optical crosstalk by whichimage resolution of the image sensor may thus be deteriorated; and thesensing images may be distorted.

In order to solve the problems, shallow trench isolation (STIs) disposedbetween two adjacent pixels have been applied to suppress the electricaland optical crosstalk. However, STIs cannot provide the image sensorenough barriers for electrical crosstalk suppression, especially in abackside illumination (BSI) image sensor, since the depth of the STIs israther limited.

Therefore, there is a need of providing an improved image sensor andmethod for fabricating the same to obviate the drawbacks encounteredfrom the prior art.

SUMMARY

According to one aspect of the present invention is to provide an imagesensor, wherein the image sensor includes a semiconductor substrate, aplurality of photoelectric transducer devices and a dielectric isolatingstructure. The semiconductor substrate has a backside surface and afront side surface opposite to the backside surface. The photoelectrictransducer devices are disposed on the front side surface. Thedielectric isolating structure extends downwards into the semiconductorsubstrate from the front side surface and penetrates through thebackside surface, so as to from a grid structure and to isolate thephotoelectric transducer devices from each other.

According to another aspect of the present invention, a method forfabricating an image sensor is disclosed, wherein the method includessteps as follows: Firstly, a semiconductor substrate having a pluralityof photoelectric transducer devices and a dielectric isolating structureis provided, wherein the semiconductor substrate has a backside surfaceand a front side surface opposite to the backside surface; thephotoelectric transducer devices are disposed on the front side surface;and the dielectric isolating structure extends downwards into thesubstrate from the front side surface and penetrating through thebackside surface, so as to isolate the photoelectric transducer devicesfrom each other. Subsequently, a portion of the semiconductor substrateis removed from the backside surface to expose a portion of thedielectric isolating structure, so as to form a grid structureprotruding from the backside surface.

In accordance with the aforementioned embodiments of the presentinvention, an image sensor and method for fabricating the same areprovided. In some embodiments, a dielectric isolating structure isformed at a front side surface of a semiconductor substrate andextending downwards into the semiconductor substrate in a manner ofdividing the semiconductor substrate into a plurality of sub-pixelregions. Next, at least one photoelectric transducer device is formed oneach of the sub-pixel regions. Subsequently, a portion of thesemiconductor substrate is removed from the backside surface to expose aportion of the dielectric isolating structure, so as to form a gridstructure protruding from the backside surface of the semiconductorsubstrate.

Since incident light coming from external circumstances, passing throughthe backside surface of the semiconductor substrate and directed todifferent sub-pixel regions can be confined in the correspondingsub-pixel region by the grid structure, and the photoelectric transducerdevices are isolated from each other by the dielectric isolatingstructure, thus the photo-carriers generated by the photoelectrictransducer devices disposed in one of the isolated sub-pixel regionscannot crosstalk with that generated by the photoelectric transducerdevices disposed in the other sub-pixel regions adjacent to the isolatedone.

In addition, because the grid structure is one portion of the dielectricisolating structure that is exposed from the backside surface of thesubstrate. The grid structure and the dielectric isolating structure canbe regarded as an integrated structure formed by the same patterningprocess with an identical reticle. In other words, the grid structurecan be form on the backside surface of the substrate without usingadditional reticles and alignment marks. As a result, the process forfabricating the image sensor can be simplified; more precise processcontrol and reduced manufacturing cost can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore readily apparent to those ordinarily skilled in the art afterreviewing the following detailed description and accompanying drawings,in which:

FIGS. 1A-1G are cross-sectional views illustrating the process forfabricating a MOS image sensor in accordance with one embodiment of thepresent invention;

FIG. 2 is a top view illustrating a grid structure in accordance withone embodiment of the present invention;

FIGS. 3A-3C are cross-sectional views partially illustrating the processfor fabricating a MOS image sensor in accordance with another embodimentof the present invention;

FIGS. 4A-4D are cross-sectional views partially illustrating the processfor fabricating a MOS image sensor in accordance with yet anotherembodiment of the present invention; and

FIGS. 5A-5C are cross-sectional views partially illustrating the processfor fabricating a MOS image sensor in accordance with yet anotherembodiment of the present invention.

DETAILED DESCRIPTION

The embodiments as illustrated below provide an image sensor and themethod for fabricating the same to solve the problems of electrical andoptical crosstalk encountered from the prior art. The present inventionwill now be described more specifically with reference to the followingembodiments and accompanying drawings illustrating the structure andmethod for fabricating the image sensor.

It is to be noted that the following descriptions of preferredembodiments of this invention are presented herein for purpose ofillustration and description only. It is not intended to be exhaustiveor to be limited to the precise form disclosed. Also, it is alsoimportant to point out that there may be other features, elements, stepsand parameters for implementing the embodiments of the presentdisclosure which are not specifically illustrated. Thus, thespecification and the drawings are to be regard as an illustrative senserather than a restrictive sense. Various modifications and similararrangements may be provided by the persons skilled in the art withinthe spirit and scope of the present invention. In addition, theillustrations may not be necessarily be drawn to scale, and theidentical elements of the embodiments are designated with the samereference numerals.

FIGS. 1A-1G are cross-sectional views illustrating the process forfabricating a MOS image sensor 100 in accordance with one embodiment ofthe present invention. Firstly, a semiconductor substrate 101 isprovided (see FIG. 1A). In some embodiments of the present invention,the semiconductor substrate 101 may be made of a semiconductor material,such as silicon (Si), germanium (Ge) or a compound semiconductormaterial, such as gallium arsenide (GaAs). In some other embodiments ofthe present invention, the semiconductor substrate 101 may be asilicon-on-insulator (SOI) wafer. In the present embodiment, thesemiconductor substrate 101 preferably is a Si wafer.

A dielectric isolating structure 103 is then formed in the semiconductorsubstrate 101 to divide the semiconductor substrate 101 into a pluralityof sub-pixel regions 104. In the present embodiment, the dielectricisolating structure 103 is a deep trench isolation structure. Theforming of the dielectric isolating structure 103 includes steps asfollows: An etching process, such as a reactive ion etching (RIE)process, is firstly performed on the front side surface 101 a of thesemiconductor substrate 101, to form at least one trench(es) 106extending downwards into the semiconductor substrate 101 from the frontside surface 101 a of the semiconductor substrate 101, so as to dividethe semiconductor substrate 101 into a plurality of sub-pixel regions104 (see FIG. 1B).

Next, a dielectric material 107 is formed on the front side surface 101a of the semiconductor substrate 101 to fill the trenches 106. In someembodiments of the present invention, each of the trenches 106 has adepth substantially less than the thickness of the semiconductorsubstrate 101. In other words, the trenches 106 does not penetratingthrough the backside surface 101 b of the semiconductor substrate 101(see FIG. 10). The dielectric material 107 may be an anti-reflectingmaterial including silicon oxide and may be filled in the trenches 106with a single layer structure or a multi-layer structure. In the presentembodiment, the dielectric material 107 may include silicon dioxide(SiO₂). The dielectric isolating structure 103 made of the dielectricmaterial 107 is a deep trench isolation structure configured by onesingle layer of anti-reflecting material including SiO₂, or a deeptrench isolation structure configured by multi-layers of anti-reflectingmaterial including a SiO₂/silicon nitride (SiN)/SiO₂/SiN/SiON stackedstructure.

A series front side processes are then performed on the front sidesurface 101 a of the semiconductor substrate 101 to form at least onephotoelectric transducer device 102, wire connection and at least onepad 105 on each of the sub-pixel regions 104 (see FIG. 1D). In someembodiments of the present invention, each of the sub-pixel regions 104that are separated by the dielectric isolating structure 103 may havesingle one photoelectric transducer device 102. However, in some otherembodiments of the present invention, each of the sub-pixel regions 104that are separated by the dielectric isolating structure 103 may have aplurality of photoelectric transducer devices 102.

The forming of the photoelectric transducer devices 102 comprises stepsas follows: a plurality of ion implantation process are performed on thefront side surface 101 a of the semiconductor substrate 101 to form atleast one photo diode (PD) 102 a and a floating drain region 102 b ateach of the sub-pixel regions 104, wherein the floating drain region 102b is corresponding to and separated from the PD 102 a. Subsequently, agate structure 102 c corresponding to the PD 102 a and the PD 102 a isformed at each of the sub-pixel regions 104 on the front side surface101 a of the semiconductor substrate 101, wherein the gate structure 102c is disposed adjacent to the PD 102 a and the PD 102 b.

Next, a portion of the semiconductor substrate 101 is removed from thebackside surface 101 b to expose a portion of the dielectric isolatingstructure 103, so as to form a grid structure 108 protruding from thebackside surface 101 b of the semiconductor substrate 101 (see FIG. 1E).In some embodiments of the present invention, the process for removingthe portion of the semiconductor substrate 101 includes steps asfollows: A thinning process, such as a chemical-mechanical polishing(CMP), is firstly performed on the backside surface 101 b of thesemiconductor substrate 101 to thin down the semiconductor substrate101, so as to make the semiconductor substrate 101 has a thicknesssubstantially less than 3 μm. An etching process is then performed onthe backside surface 101 b of the thinned semiconductor substrate 101 toremove a portion of the semiconductor substrate 101. For example, a wetetching process using tetramethylammonium hydroxide (TMAH) orhydrofluoric acid/nitric acid/acetic acid solution (HNA) as the etchantis performed on the backside surface 101 b of the semiconductorsubstrate 101 to remove a portion of the semiconductor substrate 101from the backside surface 101 b, so as to expose a portion of thedielectric isolating structure 103 and to regard to the exposed portionof the dielectric isolating structure 103 as the grid structure 108.

The grid structure 108 formed by the wet etching process includes aframe portion 108 a consisting of the exposed portion of the dielectricisolating structure 103 and a plurality of recess portions 108 b definedby the frame portion 108 a and the backside surface 101 b of thesemiconductor substrate 101, wherein each of the recess portions 108 bis corresponding to one of the sub-pixel region 104. For example, FIG. 2is a top view illustrating a grid structure 108 in accordance with oneembodiment of the present invention. In the present embodiment, the gridstructure 108 may be arranged with rows and columns to form a chessboardstructure. However, the arrangement of the grid structure 108 may notlimited in this regard. In other embodiments, the arrangement of thegrid structure 108 may varied in accordance with different layoutdesigns (topographies) of the photoelectric transducer devices 102.

Thereinafter, a color filter (CF) 109 is formed on the grid structure108 and the backside surface 101 b of the semiconductor substrate 101,and a plurality of micro lenses 110 are then formed on the CF 109. Inthe present embodiment, the CF 109 includes a plurality of colorfiltering elements, e.g. including three color filtering elements 109R,109G and 109B; and each one of which is corresponding to each of thesub-pixel regions 104. For example, each of the sub-pixel regions 104may have one color filtering element; and the color filtering elements109R, 109G and 109B may at least partially extend into the correspondingrecess portion 108 b of the grid structure 108 (see FIG. 1F). The microlenses 110 preferably are made of glass, polymer and plastic material(such as, epoxy), propylene glycol mono-methyl ether acetate (PGMEA) orthe arbitrary combinations thereof.

After a series of back-end-of-line (BEOL) processes, such as a metaldamascene process used to form a metal interconnection structure 111 onthe front surface 101 a of the semiconductor substrate 101, a metalwiring process and a chip packing process, are subsequently performed,the image sensor 100 as shown in FIG. 1G can be accomplished. In thepresent embodiment, the metal interconnection structure 111 includes aplurality of metal wire layout layers 111 a and a plurality of via plugs111 b used to electrically connect the metal wire layout layers 111 aand the pads 105.

Incident light L coming from external circumstances, passing through thebackside surface 101 b of the semiconductor substrate 101 and thendirected to each of the sub-pixel regions 104 can be shielded andreflected by the grid structure 108 protruding from the backside surface101 b and the portion of the dielectric isolating structure 103 buriedin the semiconductor substrate 101, whereby the incident light L can beconfined in the corresponding sub-pixel regions 104, and opticalcrosstalk occurring between different sub-pixel regions 104 can beavoided. In addition, since the photoelectric transducer devices 102 areisolated from each other by the dielectric isolating structure 103, thusthe photo-carriers generated by the photoelectric transducer devices 102disposed in one of the isolated sub-pixel regions 104 cannot crosstalkwith that generated by the photoelectric transducer devices 102 disposedin the other sub-pixel regions 104 adjacent to the isolated one.

FIGS. 3A-3C are cross-sectional views partially illustrating the processfor fabricating a MOS image sensor 300 in accordance with anotherembodiment of the present invention. The structure of the MOS imagesensor 300 and the process for fabricating the same are similar to thatof the MOS image sensor 100, except that the MOS image sensor 300further includes spacers 305 a formed on the grid structure 108 prior tothe forming of the CF 109. Since the processing steps prior to theforming of the grid structure 108 has described above, thus theidentical elements and processing steps will not be redundantly repeatedhere, and the process for fabricating the MOS image sensor 300 may startto describe form the forming of the spacers 305 a.

In the present embodiment, the forming of the spacer 305 a includessteps as follows: Firstly, an insulating layer 312 and a capping layer305 are formed in sequence on the structure depicted in FIG. 1E toblanket over the frame portion 108 a of the grid structure 108 and theportion of the backside surface 101 b of the semiconductor substrate 101used to define the recess portions 108 b of the grid structure 108 (seeFIG. 3A). An anisotropic etching process, such as a RIE process, is thenperformed to remove a portion of the capping layer 305, so as to form aplurality of spacers 305 a on the sidewalls of the frame portion 108 aof the grid structure 108 (see FIG. 3B). In some embodiments of thepresent invention, the insulating layer 312 may be a SiO₂ layer or a SiNlayer. The spacers 305 a are made of a light shielding material selectedfrom a group consisting of metal (such as, copper (Cu), silver (Ag),aluminum (Al), titanium (Ti), tungsten (W), tantalum (Ta) etc.), metaloxide (such as, hafnium oxide (HfO₂), tantalum pentoxide (Ta₂O₅) etc.),metal nitride (such as, titanium nitride (TiN) etc.), alloys (such as,aluminum alloys) and the arbitrary combinations thereof.

Thereinafter, a CF 109 is formed on the grid structure 108 and thebackside surface 101 b of the semiconductor substrate 101, and aplurality of micro lenses 110 are then formed on the CF 109. After aseries of back-end-of-line (BEOL) processes, such as a metal damasceneprocess used to form a metal interconnection structure 111 on the frontsurface 101 a of the semiconductor substrate 101, a metal wiring processand a chip packing process, are subsequently performed, the image sensor300 as shown in FIG. 3C can be accomplished.

Incident light L coming from external circumstances, passing through thebackside surface 101 b of the semiconductor substrate 101 and thendirected to each of the sub-pixel regions 104 can be shielded andreflected by the grid structure 108 protruding from the backside surface101 b, the spacers 305 a and the portion of the dielectric isolatingstructure 103 buried in the semiconductor substrate 101, whereby theincident light L can be confined in the corresponding sub-pixel regions104, and optical crosstalk occurring between different sub-pixel regions104 can be avoided. In addition, since the photoelectric transducerdevices 102 are isolated from each other by the dielectric isolatingstructure 103, thus the photo-carriers generated by the photoelectrictransducer devices 102 disposed in one of the isolated sub-pixel regions104 cannot crosstalk with that generated by the photoelectric transducerdevices 102 disposed in the other sub-pixel regions 104 adjacent to theisolated one.

FIGS. 4A-4D are cross-sectional views partially illustrating the processfor fabricating a MOS image sensor 400 in yet accordance with anotherembodiment of the present invention. The structure of the MOS imagesensor 400 and the process for fabricating the same are similar to thatof the MOS image sensor 100, except that the dielectric isolatingstructure 403 of the MOS image sensor 400 is different from that of theMOS image sensor 100. Since the processing steps prior to the forming ofdielectric isolating structure 403 has described above, thus theidentical elements and processing steps will not be redundantly repeatedhere, and the process for fabricating the MOS image sensor 400 may startto describe form the forming of the dielectric isolating structure 403.

In the present embodiment, the forming of the dielectric isolatingstructure 403 includes steps as follows: Firstly, a first dielectriclayer 403 a is formed on the structure depicted in FIG. 1B to blanketover the sidewalls 106 a and bottoms 106 b of the trenches 106 (see FIG.4A). An embedded light shielding layer 403 b is then formed on the firstdielectric layer 403 a (see FIG. 4B). A second dielectric layer 403 c isnext formed on the embedded light shielding layer 403 b to make theembedded light shielding layer 403 b disposed between the firstdielectric layer 403 a and the second dielectric layer 403 c (see FIG.4C).

In some embodiments of the present invention, the first dielectric layer403 a and the second dielectric layer 403 c may be two single layerstructures respectively made of SiO₂ and SiN. In some other embodiments,the first dielectric layer 403 a and the second dielectric layer 403 cmay be two SiO₂/SiN or SiO₂/SiON bilayer structures. In yet otherembodiments, the first dielectric layer 403 a and the second dielectriclayer 403 c may be two multi-layer structures, such as two SiO₂/SiN/SiO₂or SiO₂/SiON/SiO₂ tri-layer structures. The embedded light shieldinglayer 403 b can be made by a material selected from a group consistingof SiN, SiON, poly-silicon, metal (such as, Cu, Ag, Al, Ti, W, Ta etc.),metal oxide (such as, HfO₂, Ta₂O₅ etc.), metal nitride (such as, TiNetc.) and the arbitrary combinations thereof.

A series front side processes are then performed on the front sidesurface 101 a of the semiconductor substrate 101 to form at least onephotoelectric transducer device 102 on each of the sub-pixel regions104. Next, a portion of the semiconductor substrate 101 is removed fromthe backside surface 101 b to expose a portion of the dielectricisolating structure 403, so as to form a grid structure 408 protrudingfrom the backside surface 101 b of the semiconductor substrate 101.Thereinafter, a CF 109 is formed on the grid structure 408 and thebackside surface 101 b of the semiconductor substrate 101, and aplurality of micro lenses 110 are then formed on the CF 109.Subsequently, after a series of back-end-of-line (BEOL) processes, suchas a metal damascene process used to form a metal interconnectionstructure 111 on the front surface 101 a of the semiconductor substrate101, a metal wiring process and a chip packing process, are performed,the image sensor 400 as shown in FIG. 4D can be accomplished.

Incident light L coming from external circumstances, passing through thebackside surface 101 b of the semiconductor substrate 101 and thendirected to each of the sub-pixel regions 104 can be shielded andreflected by the grid structure 408 protruding from the backside surface101 b and the portion of the dielectric isolating structure 403 buriedin the semiconductor substrate 101, whereby the incident light L can beconfined in the corresponding sub-pixel regions 104, and opticalcrosstalk occurring between different sub-pixel regions 104 can beavoided. In addition, since the photoelectric transducer devices 102 areisolated from each other by the dielectric isolating structure 403, thusthe photo-carriers generated by the photoelectric transducer devices 102disposed in one of the isolated sub-pixel regions 104 cannot crosstalkwith that generated by the photoelectric transducer devices 102 disposedin the other sub-pixel regions 104 adjacent to the isolated one.

FIGS. 5A-5C are cross-sectional views partially illustrating the processfor fabricating a MOS image sensor 500 in yet accordance with anotherembodiment of the present invention. The structure of the MOS imagesensor 500 and the process for fabricating the same are similar to thatof the MOS image sensor 100, except that the dielectric isolatingstructure 503 of the MOS image sensor 500 is different from that of theMOS image sensor 100. Since the processing steps prior to the forming ofdielectric isolating structure 503 has described above, thus theidentical elements and processing steps will not be redundantly repeatedhere, and the process for fabricating the MOS image sensor 500 may startto describe form the forming of the dielectric isolating structure 503.

In the present embodiment, the forming of the dielectric isolatingstructure 503 includes steps as follows: Firstly, a light shieldingliner 503 a is formed on the structure depicted in FIG. 1B to blanketover the sidewalls 106 a and bottoms 106 b of the trenches 106 (see FIG.5A). Next, a dielectric material 107 is formed to fill the trenches 106(see FIG. 5B). The light shielding liner 503 a can be made by a materialselected from a group consisting of SiN, poly-silicon, metal oxide (suchas, HfO₂, Ta₂O₅ etc.), metal nitride (such as, TiN etc.) and thearbitrary combinations thereof.

A series front side processes are then performed on the front sidesurface 101 a of the semiconductor substrate 101 to form at least onephotoelectric transducer device 102 on each of the sub-pixel regions104. Next, a portion of the semiconductor substrate 101 is removed fromthe backside surface 101 b to expose a portion of the dielectricisolating structure 503, so as to form a grid structure 508 protrudingfrom the backside surface 101 b of the semiconductor substrate 101.Thereinafter, a CF 109 is formed on the grid structure 508 and thebackside surface 101 b of the semiconductor substrate 101, and aplurality of micro lenses 110 are then formed on the CF 109.Subsequently, after a series of back-end-of-line (BEOL) processes, suchas a metal damascene process used to form a metal interconnectionstructure 111 on the front surface 101 a of the semiconductor substrate101, a metal wiring process and a chip packing process, are performed,the image sensor 500 as shown in FIG. 5C can be accomplished.

Incident light L coming from external circumstances, passing through thebackside surface 101 b of the semiconductor substrate 101 and thendirected to each of the sub-pixel regions 104 can be shielded andreflected by the grid structure 508 protruding from the backside surface101 b and the portion of the dielectric isolating structure 503 buriedin the semiconductor substrate 101, whereby the incident light L can beconfined in the corresponding sub-pixel regions 104, and opticalcrosstalk occurring between different sub-pixel regions 104 can beavoided. In addition, since the photoelectric transducer devices 102 areisolated from each other by the dielectric isolating structure 503, thusthe photo-carriers generated by the photoelectric transducer devices 102disposed in one of the isolated sub-pixel regions 104 cannot crosstalkwith that generated by the photoelectric transducer devices 102 disposedin the other sub-pixel regions 104 adjacent to the isolated one.

In accordance with the aforementioned embodiments of the presentinvention, an image sensor and method for fabricating the same areprovided. In some embodiments, a dielectric isolating structure isformed at a front side surface of a semiconductor substrate andextending downwards into the semiconductor substrate in a manner ofdividing the semiconductor substrate into a plurality of sub-pixelregions. Next, at least one photoelectric transducer device is formed oneach of the sub-pixel regions. Subsequently, a portion of thesemiconductor substrate is removed from the backside surface to expose aportion of the dielectric isolating structure, so as to form a gridstructure protruding from the backside surface of the semiconductorsubstrate. A CF 109 and a plurality of micro lenses are then formed onthe grid structure 108 and the backside surface 101 b of thesemiconductor substrate in sequence, wherein the CF extends into thegrid structure 108.

Since incident light coming from external circumstances, passing throughthe backside surface of the semiconductor substrate and directed todifferent sub-pixel regions can be confined in the correspondingsub-pixel region by the grid structure, and the photoelectric transducerdevices are isolated from each other by the dielectric isolatingstructure, thus the photo-carriers generated by the photoelectrictransducer devices disposed in one of the isolated sub-pixel regionscannot crosstalk with that generated by the photoelectric transducerdevices disposed in the other sub-pixel regions adjacent to the isolatedone.

In addition, because the grid structure is one portion of the dielectricisolating structure that is exposed from the backside surface of thesubstrate. The grid structure and the dielectric isolating structure canbe regarded as an integrated structure formed by the same patterningprocess with an identical reticle. In other words, the grid structurecan be form on the backside surface of the substrate without usingadditional reticles and alignment marks. As a result, the process forfabricating the image sensor can be simplified; more precise processcontrol and reduced manufacturing cost can be obtained.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed embodiments.It is intended that the specification and examples be considered asexemplary only, with a true scope of the invention being indicated bythe following claims and their equivalents.

1. An image sensor, comprising: a semiconductor substrate having abackside surface and a front side surface opposite to the backsidesurface; a plurality of photoelectric transducer devices disposed on thefront side surface; a dielectric isolating structure extending downwardsinto the semiconductor substrate from the front side surface andpenetrating through the backside surface, so as to from a grid structureand isolate the photoelectric transducer devices from each other; and acolor filter (CF) formed on the grid structure and directly in contactwith the semiconductor substrate.
 2. The image sensor according to claim1, wherein the grid structure and the semiconductor substrate defines aplurality of recesses and each of the recesses is corresponding to asub-pixel region.
 3. The image sensor according to claim 2, furthercomprising a plurality of micro lenses disposed on the CF at leastpartially extending into the recesses.
 4. The image sensor according toclaim 1, further comprising an embedded light shielding layer embeddedin the dielectric isolating structure.
 5. The image sensor according toclaim 4, wherein the dielectric isolating structure further comprises afirst dielectric layer and a second dielectric layer; and the embeddedlight shielding layer is disposed between the first dielectric layer andthe second dielectric layer.
 6. The image sensor according to claim 4,wherein the dielectric isolating structure comprises silicon oxide, andthe embedded light shielding layer comprises a material selected from agroup consisting of silicon nitride (SiN), silicon oxynitride (SiON),poly-silicon and arbitrary combinations thereof.
 7. The image sensoraccording to claim 1, further comprising a light shielding liner blanketover a plurality of sidewalls of the dielectric isolating structure. 8.The image sensor according to claim 7, wherein the dielectric isolatingstructure comprises silicon oxide and the light shielding linercomprises SiN.
 9. The image sensor according to claim 1, furthercomprising a plurality of spacers disposed on a plurality of sidewallsof the grid structure.
 10. The image sensor according to claim 9,wherein the spacers comprises a light shielding material selected from agroup consisting of metal, metal oxide, metal nitride, alloys andarbitrary combinations thereof.
 11. The image sensor according to claim9, wherein the spacers comprises a metal material selected from a groupconsisting of copper (Cu), silver (Ag), aluminum (Al), titanium (Ti),tungsten (W), tantalum (Ta) and arbitrary combinations thereof.
 12. Theimage sensor according to claim 1, wherein each of the photoelectrictransducer devices comprises: a photo diode (PD) disposed in thesemiconductor substrate; a floating drain region disposed in thesemiconductor substrate and separated from the PD; and a gate structuredisposed on the front side surface of the semiconductor substrate andadjacent to the PD and the floating drain region.
 13. The image sensoraccording to claim 1, further comprising a metal interconnectionstructure disposed on the front side surface and electrically connectedto the photoelectric transducer devices.
 14. A method for fabricating animage sensor, comprising: providing a semiconductor substrate having aplurality of photoelectric transducer devices and a dielectric isolatingstructure, wherein the semiconductor substrate has a backside surfaceand a front side surface opposite to the backside surface; thephotoelectric transducer devices are disposed on the front side surface;and the dielectric isolating structure extends downwards into thesemiconductor substrate from the front side surface and penetratesthrough the backside surface, so as to isolate the photoelectrictransducer devices from each other; and removing a portion of thesemiconductor substrate from the backside surface to expose a portion ofthe dielectric isolating structure, so as to form a grid structureprotruding from the backside surface.
 15. The method according to claim14, wherein the process for removing the portion of the semiconductorsubstrate comprises a wet etching process.
 16. The method according toclaim 14, wherein the process for forming the dielectric isolatingstructure comprises: forming a plurality of extending downwards into thesemiconductor substrate from the front side surface of the semiconductorsubstrate; forming a first dielectric layer to blanket over a pluralityof sidewalls of the trenches; forming an embedded light shielding layeron the first dielectric layer; and forming a second dielectric layer onthe embedded light shielding layer to make the embedded light shieldinglayer disposed between the first dielectric layer and the seconddielectric layer.
 17. The method according to claim 14, wherein theprocess for forming the dielectric isolating structure comprises:forming a plurality of trenches extending downwards into thesemiconductor substrate from the front side surface of the semiconductorsubstrate; forming a light shielding liner to blanket over a pluralityof sidewalls of the trenches; and filling the trenches with a dielectricmaterial.
 18. The method according to claim 14, further comprising:forming a capping layer to blanket over the grid structure and thebackside surface of the semiconductor substrate; and removing a portionof the capping layer to form a plurality of spacers on a plurality ofsidewalls of the dielectric isolating structure.
 19. The methodaccording to claim 14, further comprising: forming a CF on the gridstructure and the backside surface of the semiconductor substrate; andforming a plurality of micro lenses on the CF.
 20. The method accordingto claim 14, wherein the process for forming the photoelectrictransducer devices comprises: forming a photo diode PD and a floatingdrain region separated from the PD in the semiconductor substrate; andforming a gate structure on the front side surface of the semiconductorsubstrate and adjacent to the PD and the floating drain region.